REPORT OF THE SOCIETY 17 



tions concerning the hydrogen-ion concentration and natural immunity of 

 plants found that injections of pathogenic bacteria cause the plants to respond 

 with variations in the hj^drogen-ion concentration. Immediately after infection 

 the acidity decreases. At the end of the incubation period the acidity rises. 

 If the plant is able to withstand the infection the acidity then falls back to 

 normal. If the plant is unable to withstand the infection,. hydrogen-ion con- 

 centration rises to a very high level, and then falls, usually below normal! 



Other cell contents besides those already discussed appear to account for 

 some cases of resistance. Biologic species of parasitic fungi are known to be 

 very sensitive to the minutes differences in the albumen contents of the host 

 plants. This may explain with some varities of plants are resistant to certain 

 biologic strains and not to others. Walker in his researches on disease resistance 

 to onion smudge, found that some substance (or substances) closely associated, 

 or identical with, the yellow and red pigments found in the cells of the other 

 scales of the resistant bulbs, was evidently the chief cause of resistance to onion 

 smudge (2) (Colletotrichum circinans). It has been found that the leaves of 

 certain species of oak immune to powdery mildew have a smaller soluble nitro- 

 gen content than the leaves of susceptible species (3). The paper by Lepschkin 

 on the "Influence of Vitamir.es upon the development of yea&ts and moulds" (4) 

 makes one speculate as to the part that these vital substances may play in 

 resistance in plants. This is a field of future reasearch for the bio-chemist. 



Our present knowledge of immunity and resistance in plants would seem 

 to warrant the following statements. 



First. — That substantial and permanent progress has been made in the 

 production and selection of resistant varieties of plants. 



Second. — That further and more extensive studies concerning the existence 

 of biologic straims of different parastitic fungi are required. 



Third. — That our knowledge concerning the bio-chemical causes of resis- 

 tance is fragmentary and disconnected. 



Fourth. — That future reaserch work on this subject lies largely in the filed 

 of bio-chemistry. 



1. Popp M. Centralb. Bakt. 33: 707-719, 1916. 



2. Walker, J. C. Jour. Agr. Res. 24, No 12, Jo. 1923. 



3. Mont martini, L. Rev. Pat. Veg 9: 72-79. 1919. 



4. Lepeshkin, W. Amer. Jour. Bot. 11, 169-189, March 1924 



